As a tobacco filter which provides for the effective removal of harmful components of the tobacco such as tar, and insures a satisfactory smoking quality, a filter plug prepared by shaping a tow (fiber bundle) of a cellulose acetate (e.g. a cellulose acetate having an average degree of substitution of about 2.4) fiber with a plasticizer such as triacetin is known. In this filter plug, however, the biodegradability is low, and the constituent filaments have been partly fused together by the plasticizer so that when it is discarded after smoking, it takes a long time for the filter plug to disintegrate itself in the environment, thus adding to the pollution problem. Moreover, such a filter plug can hardly be completely recovered and would entail an almost prohibitive cost of recovery. Disposal of filter plugs by incinerating involves large outputs of combustion heat which detract considerably from the serviceable life of the incinerator.
Meanwhile, a tobacco filter made of a sheet-form or creped paper manufactured from a wood pulp and a tobacco filter made from a regenerated cellulose fiber are also known. Compared with a filter plug comprising a tow (fiber bundle) of a cellulose acetate fiber, these filters are meritorious in biodegradability and slightly more wet-disintegratable (wet-disintegrative) and, thus, of somewhat lower pollution potential. However, in these filters, not only are the aroma (taste) and palatability of tobacco smoke sacrificed but also the efficiency of selective elimination of phenols which is essential to tobacco filters is not acceptable when compared with the cellulose acetate filter. Moreover, the firmness or hardness of these filters is lower than that of the cellulose acetate filter on a give pressure loss basis. Furthermore, such material in the form of a sheet manufactured from a wood pulp has a low bulkiness, and hence imparting a higher bulkiness to the material in order to decrease the pressure loss causes fuzz or scuffing and low moldability.
Japanese Patent Application Laid-open No. 45468/1978 (JP-A-53-45468) corresponding to U.S. patent application Ser. No. 730,039, U.S. Pat. Nos. 4,192,838 and 4,283,186 discloses a filter material comprising a nonwoven sheet containing 5 to 35% by weight of cellulose ester fibrils with a large surface area and 65 to 95% by weight of cellulose ester short staples. Furthermore, this prior art literature mentions that a wood pulp may be incorporated in this mixture of cellulose ester fibrils and cellulose ester short staples. However, because cellulose esters can hardly be processed into fine fibrils, a special technique is required for providing the fibrils with a large surface area. Moreover, the disintegratability and biodegradability of this filter material are not sufficiently high so that the risk of pollution is substantial.
Japanese Patent Application Laid-open No. 141185/1980 (JP-A-55-141185) discloses a filter material comprising a composite sheet-like entity manufactured by sealing or adhering a sheet-like entity comprising mainly wood pulp fibers, and a sheet-like entity comprising a tow of cellulose ester derivative fibers. However, in such filter material, although somewhat improved aroma and palatability of tobacco smoke can be obtained, the molding of the sheet-like entity and the sealing or adhering of the both sheets are conducted with the use of a plasticizer such as triacetin so that the fibers and the sheets are fused to each other and fail to provide a sufficient wet disintegratability.
Furthermore, a tobacco filter material in a sheet form is occasionally subjected to creping or other processing during molding or shaping processes, and such tobacco filter material is required to retain a high dry strength during the processing or dry handling but, then, its wet disintegratability is low. By the same token, a sheet material providing for a high degree of wet disintegratability shows only a low strength even in dry handling condition.
Meanwhile, Japanese Patent Application Laid-open No. 227939/1993 (JP-A-5-227939) discloses a cigarette filter made of a biodegradable aliphatic polyester with fine pores for alleviating the pollution burden on the environment. This filter provides somewhat enhanced biodegradability. The aroma and palatability of tobacco smoke in such filter are, however, sacrificed in comparison with the cellulose acetate filter plug.
Japanese Patent Application Laid-open No. 72900/1977 (JP-A-52-72900) discloses a tobacco filter comprising an aggregate of fibrous acetylated cellulose having an average degree of acetylation in the range of 10 to 50%. This literature mentions that the fibrous acetylated cellulose is obtained by acetylating a cellulose fiber such as pulp with the use of a catalyst for acetylation such as sulfuric acid. However, the fiber obtained by such technique is not sufficient in the biodegradability yet is excellent in the aroma and palatability of tobacco smoke.
Japanese Patent Publication No. 1944/1969 (JP-B-44-1944) discloses a tobacco filter which is produced by adding a solution containing a hydrophobic polymer to a paper by means of impregnation or spraying and shaping the resultant paper into a rod-shape in order to improve the firmness and elasticity (springiness) of paper filters. The smoking quality of such tobacco filter may probably be improved. However, since the constituent fibers or other component of the paper are adhered or coated due to the addition of the hydrophobic polymer, the wet disintegratability of the filter is remarkably sacrificed.
Thus, excellent characteristics for a tobacco filter such as good smoking quality, the high elimination efficiency of harmful components and the high dry strength, and high biodegradability and/or wet disintegratability can hardly be reconciled in a conventional tobacco filter.